The idea is to preload the association when selecting all comments. Now, that association is only present on a sub-class of the queried class, but since it is a single table inheritance, Doctrine should be able to join it for those entities where it is present.

At the moment unfortunately, Doctrine shows an error that the association does not exist on the AbstractComment class. Also, there is no real alternative to this except moving the collection to the base class even if it does not belong there.